This invention relates to the analysis of the functioning of the brain, and, more particularly, to the analysis of the functioning of the thalamus by measurements made on the cortex of the brain.
Many of the most baffling disorders of the human body are associated with disorders of the brain. Examples include epilepsy, schizophrenia, Parkinson's disease, and chronic depression. Such disorders are difficult to analyze, understand, and treat, in part because it is not clear in some cases whether they are physical or non-physical in origin, or involve a complex interweaving of physical and non-physical causes. One of the great challenges in modern medicine is to analyze the nature and origin of these disorders, understand the mechanism of the disorders, and then treat the disorders.
In some cases, the disorders appear to involve malfunctions in a portion of the brain of a person, the manifestation of which is a so-called positive symptom. Typical positive symptoms include tremor, pain, or seizure. In some of these cases, it has been possible to alleviate the positive symptom by disrupting the communications paths between the different parts of the brain. This disruption thus provides a significant improvement in the quality of life for that person.
The thalamus is a portion of the brain which is central to the communication between the cortex, where higher sensory, motor, and cognitive functions are located, and the remainder of the body. Therefore, it has been a focus of attention for the development of therapies which address various disorders and various positive symptoms. Different physical locations in the thalamus where these abnormal rhythms occur appear to be associated with different disorders or positive symptoms. For example, it has been observed that certain positive symptoms appear to be characterized by the occurrence of characteristic patterns of electrical activity (such as abnormal low-frequency rhythmic electrical voltages) in certain groups of cells within the thalamus, and that the destruction of these cells through a surgical procedure such as a thalamotomy produces a marked reduction of the positive symptoms. Another example of therapy targeted at the thalamus is the use of electrical stimulators implanted within the thalamus of persons suffering from Parkinson's tremor. When properly placed, activation of the stimulator has been observed to arrest the tremor.
The association of brain disorders with specific locations in the thalamus has been determined largely by invasive studies using electrical probes inserted into the brain of a patient undergoing brain surgery. No techniques are available for determining these locations non-invasively and prior to surgery. Methods such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) detect secondary effects of the disorder such as oxygen concentration or metabolism rather than the primary functional activity of the disorder itself. Current electroencephalography (EEG) procedures, while detecting basic functional activity of the disorder, lack the capability to associate the measured voltages to the precise physical locations of the sources of those voltages within the brain to resolutions of a few millimeters, because of the electrical resistivity of the tissue making up the brain, skull, and scalp. Magnetoencephalography (MEG) also detects the basic functional activity of the disorder and also has the ability to determine the locations within the brain more accurately than EEG owing to the transparency of the tissues making up the head to magnetic fields. However, the rapid decay of the magnitude of magnetic signals with distance from the source (typically falling off as the inverse square of the distance) limits the practical sensitivity of that technique primarily to cortical sources. (Electrical signals also rapidly decay with distance, so EEG suffers from this same limitation.) The thalamus is located in the central region of the brain, and therefore sources in the thalamus are not readily measurable by MEG or EEG.
A non-invasive approach for observing and providing information about abnormal electrical activity occurring in the central region of the brain to within a fine spatial resolution would enable physicians to determine whether a patient suffering from a particular brain disorder might be a candidate for therapy aimed at that central region without an invasive procedure for the purposes of the determination. If the patient were such a candidate, this approach could also provide information as to where to target an appropriate therapy and which therapeutic approach is optimal.
Thus, there is needed a technique for noninvasively measuring and analyzing dysfunctional activity associated with specific locations of the thalamus or other portions of the central region of the brain. Once such a technique is available, there would be an associated opportunity for treating the disorder. The present invention fulfills these needs, and further provides related advantages.